Gram-Positive Bacteria: Characteristics, Benefits and Risks

Gram-positive bacteria are the bacteria that yield positive results in a gram stain test. In the gram stain test, these bacteria retain the color of the crystal violet stain used during the gram staining test.

• After gram staining, they appear purple-colored when examined under a microscope.
• Examples of gram-positive bacteria include staphylococci, actinomyces, mycobacterium, clostridium, and Nocardia.
• These bacteria are both useful in some cases and harmful in different cases. 
• Gram staining is a procedure to classify bacteria in two types- positive and negative.

Read Also: Difference Between Gram-Positive and Gram-Negative Bacteria

What is Gram-Positive Bacteria?

[Click Here for Sample Questions]

Gram-positive bacteria are the bacteria that possess thick cell walls and give positive result in Gram stain test, w stain used in the test, which is used to classify bacteria into two broad categories based on their type of cell wall. Moreover, gram-positive vacteria turn cystal violet stain, which then appears to be purple-coloured when seen through an optical microscope. However, gram-negative bacteria fail to retain the violet stain after the decolorization step.

Gram-positive bacteria

---

Characteristics of Gram-Positive Bacteria

[Click Here for Sample Questions]

Generally, gram-positive bacteria are having the following characteristics.

• They have a complex cell wall that consists of peptidoglycan, teichoic acids, polysaccharides, and proteins and this cell wall surrounds the cytoplasmic membrane.
• They lack an outer membrane.
• They have a thick peptidoglycan layer that is 40 to 80 layers thick.
• They have cilia and flagella and rarely contain hair-like structures called pili for locomotion.

Characteristics of Gram-Positive Bacteria

---

Gram-Positive Cell Wall

[Click Here for Sample Questions]

The cell wall structure of gram-positive bacteria is having the periplasmic space surrounded by a plasma membrane and a thick peptidoglycan layer. It has a thickness of 15 to 80 nanometers. This thick cell wall has a composition of several peptidoglycan layers, highly crosslinked peptide chains, and a glycan backbone-based structure. Peptidoglycan layers protect the cell from the environment.

• Teichoic acids are present in the gram-positive cell wall.
• These acids make up about 50% of the total dry weight of the cell wall.
• These acids are anionic polyphosphate polymers that provide rigidity to the cell wall.
• They do it either by anchoring to the plasma membrane or via the covalent bonding to peptidoglycan.
• Anionic polymers that are present in the cell wall of the gram-positive bacteria also have a similar function as that of teichoic acid.
• Anionic polymers do so by influencing permeability, mediating interactions, and acting as a scaffold for extracytoplasmic enzymes.
• Cell wall is made up of following components.

Gram-Positive Cell Wall

Read Also: Difference Between Cell and Tissue

Peptidoglycan 

It is a permeable, cross-linked organic polymer and rigid structure which plays an integral part in providing shape and strength to the cell wall. It makes up about 90% of the cell wall that encloses the plasma membrane and protects the cell from the environment. Peptidoglycan is consists of three main components- Glycan backbone, Peptide, and Tetra-peptide.

Lipid 

The lipid element which is found in the gram-positive bacteria cell wall supports its anchoring to the membrane. The lipid content in a gram-positive bacterium cell wall is about 2 – 5 percentage.

Teichoic Acid

It is water-soluble and a polymer of glycerol. Teichoic acid is the major surface antigen of gram-positive bacteria that makes up about 50% of the total dry weight of the cell wall.

Read Also: Difference Between Smooth Endoplasmic Reticulum and Rough Endoplasmic Reticulum

---

Benefits of Gram-Positive Bacteria 

[Click Here for Sample Questions]

The benefits of gram-positive bacteria are listed below:

• These are the species of bacteria that reside in our body including mouth, skin, upper respiratory tract, and intestine as they are non-pathogenic.
• Various species of gram-positive bacteria are used in the secretion of large quantities of enzymes.
• Industrial production of amino acids, nucleotides, etc. is done with the help of the species of Corynebacterium.
• Bacillus amyloliquefaciens are a good source of Barnase (a natural antibiotic protein).
• Some of the species of gram-positive bacteria are also useful in cheese aging, degradation of hydrocarbons, production of Swiss cheese, etc.

Risk Factors of Gram-Positive Bacteria

[Click Here for Sample Questions]

Below are listed different types of gram-positive bacteria and defects, diseases, or risks caused by them.

• Staphylococcus bacteria grow in grape-like clusters.
• They exist in our skin and mucous membranes without causing any problem.
• But they can cause serious infections upon entering the body.
• They commonly cause bacterial infections.
• Staphylococcus aureus is the most pathogenic bacteria and is responsible for staphylococcus infections that include cellulitis, folliculitis, septic arthritis, endocarditis, bacterial pneumonia, food poisoning, etc.
• Staphylococcus epidermidis cause infections in humans with weak immune systems.
• They cause infections such as mediastinitis, bacteremia, surgical site infections, inner eye infections, etc.
• Staphylococcus saprophyticus it is normally found in the genital tract and perineum.
• It causes infections like uncomplicated urinary tract infections, prostatitis, epididymitis, acute pyelonephritis, etc.
• Streptococcus grow in chains because the cells don`t completely separate after dividing.
• They also normally exist in our body like staphylococcus.
• They can also be found in the genital tract of humans.
• They are classified into the following categories.
• S. pyogenes (group A) causes infections such as cellulitis, strep throat, scarlet fever, rheumatic fever, necrotizing fasciitis, glomerulonephritis, pharyngitis, impetigo.
• S. agalactiae (group B) causes infections in newborns that include sepsis, meningitis, pneumonia.
• Enterococci (group C) mostly cause biliary and urinary tract infections.
• S. pneumonia is the most common cause of community-acquired pneumonia disease.
• It also causes infections like pink eye, sinus infections, meningitis.

S. pneumonia

• Clostridium are about 30 species of clostridium that cause diseases in humans.
• These are usually involved in foodborne illnesses.
• Most concerning clostridium bacteria include:
  • Clostridium botulinum: the spores of this bacteria produce the most dangerous toxin called botulinum toxin that leads to botulism including infant botulism, wound botulism, inhalation botulism, and foodborne botulism.
  • Clostridium perfringens: the infections caused by these bacteria are associated with eating contaminated meat that causes food poisoning in humans.
  • The symptoms include abdominal cramps and diarrhea.
  • Clostridium difficile: it causes colitis, abdominal cramping, severe diarrhea.
  • These bacteria affect old-aged individuals in hospitals typically after taking antibiotics.
  • Clostridium tetani: its spores produce the tetanus toxin that is a neurotoxic substance.
  • Spores produced by this bacterium can be found in soil, ash, and rusty tools.
  • The infection caused by the toxin substance is called tetanus that leads to serious medical emergencies.
• Listeria monocytogenes is the only pathogenic bacteria from listeria bacteria.
• It causes life-threatening conditions in people with a weakened immune system.
• The conditions include meningitis, septicemia, listeriosis.
• Corynebacterium diphtheria it is the primary pathogenic bacteria from Corynebacterium bacteria .
• It is responsible for pharyngitis, diphtheria, cutaneous infections, osteomyelitis, endocarditis, septic arthritis.
• Bacillus  make spores that release toxins. Below are the two types of bacillus bacteria that are involved in severe medical conditions.
  • Bacillus anthracis: the spores made by B. anthracis produce the anthrax toxin that causes serious illness.
  • It can be transferred by contact with infected animals or inhalation.
  • Symptoms caused by B. anthracis depend on how it spreads.
  • The symptoms include nausea, vomiting, abdominal pain, coughing up blood, high fever, itchy bump.
  • Bacillus cereus: it is found in the soil and some foods.
  • It causes illness due to eating reheated or undercooked rice.
  • It causes diarrhea, nausea, respiratory infections, endophthalmitis-like diseases.

Things to Remember

• Gram-positive bacteria yield positive results in the gram stain test.
• It appears as purple-colored under the microscope upon gram stain test.
• Examples of gram-positive bacteria are staphylococci, actinomyces, mycobacterium, clostridium, and Nocardia
• The cell wall of Gram-positive bacteria consists of peptidoglycan, teichoic acids, polysaccharides, and proteins.
• Benefits of gram-positive bacteria include secretion of enzymes, Industrial production of amino acids, nucleotides, etc.
• Gram-positive bacteria also causes diseases and infections in humans.
• Common infections include folliculitis, septic arthritis, endocarditis, bacterial pneumonia, food poisoning etc.